1. Field of the Invention
This invention generally relates to mechanical pigging devices, commonly referred to simply as xe2x80x9cpigsxe2x80x9d, for use in pipelines or other tubulars. Such pigs are known to find utility in a diverse range of applications, including for cleaning purposes and for conveying equipment in the case, for example, of pipeline monitoring. In the present invention there is described a unique pig suitable for use in the cleaning of internal surfaces of a pipeline or tubular and, in a variation thereof, suitable for applying coatings or other fluids to the aforesaid surfaces.
2. Background of Related Art
It is known in the art to cause cleaning pigs to be propelled through a pipe or tubing under the influence of a pressurised fluid. Pigs, designed for this purpose, typically have a flexible cylindrical body made, for example, from a polyurethane foam. Other materials have also commonly been used, including rubber, metal, plastics and combinations and composites. The rear and front end walls of the cylindrical body may be covered with an impervious coating designed to form a moving seal with the inner wall of the pipe. With this design, the pig essentially acts as a piston as it is conveyed through the pipeline or tubular; the fluid on its rear side having a higher pressure head than the fluid at its front side.
Notably, pigs propelled through pipelines or the like in the manner described above are intended to prevent propelling fluid from flowing through or around the pig. Implicated by this, pigs used for cleaning purposes have, in the past, been intended to physically push and forceout debris in advance of the pig as it travels through the pipe bore. At best, the pig itself provides an additional wiping function on the pipe walls.
In the present invention it is recognised that, on occasion, it would be advantageous to provide a more rigorous cleaning process to a pipeline bore than merely pushing loose debris and wiping the surfaces. In the art, those who have addressed this problem have contemplated the provision of scratching elements, such as wire bristles, on the circumferential walls of the pig. While related designs provide for a more aggressive cleaning process, such pigs usually do not allow for sufficient fluid flow past the bristles to allow for the bristles themselves to be cleaned. In use, debris, shavings, slivers and the like can become lodged between the bristles, serving to reduce the efficiency of the pig""s travel and the cleaning process.
An object of the present invention is to obviate or at least mitigate these and other disadvantages associated with pipeline or tubular cleaning pigs. In one aspect, the invention seeks to achieve this by creating an alternative means for the propulsion of the pig through the pipeline or other tubular.
A further object of the invention herein is to employ the novel propulsion features disclosed herein in relation to pigs for use in respect of other functions, including pigs intended to act as mechanical applicators,